U.S. patent number 10,899,858 [Application Number 16/095,670] was granted by the patent office on 2021-01-26 for polyethylene material and application thereof.
This patent grant is currently assigned to CHINA PETROLEUM & CHEMICAL CORPORATION, ZHEJIANG UNIVERSITY. The grantee listed for this patent is CHINA PETROLEUM & CHEMICAL CORPORATION, ZHEJIANG UNIVERSITY. Invention is credited to Yuhui Cui, Xiaoqiang Fan, Guodong Han, Xiaobo Hu, Zhengliang Huang, Binbo Jiang, Zuwei Liao, Jingyuan Sun, Jingdai Wang, Xiaofei Wang, Wenqing Wu, Yao Yang, Yongrong Yang.
United States Patent |
10,899,858 |
Wang , et al. |
January 26, 2021 |
Polyethylene material and application thereof
Abstract
Provided is a polyethylene material and application thereof. A
density distribution of the polyethylene material is in a range of
0.880 g/cm.sup.3-0.960 g/cm.sup.3. An amount of a fraction at a
temperature of 40.degree. C. obtained by conducting temperature
rising elution fractionation on the polyethylene material is in a
range of 9.0 wt %-40.0 wt %, preferably in a range of 10.0 wt
%-25.0 wt %, more preferably in a range of 9.9 wt %-20.0 wt %. A
melting temperature of the polyethylene material is 110.degree.
C.-135.degree. C., preferably 116.degree. C.-130.degree. C. The
polyethylene material provided by the present application has
distinctly improved amount of medium/low-molecular-weight fractions
and high-degree-branching fractions, as well as relatively
high-molecular-weight fractions which are highly branched. The
polyethylene material thus has a relative high melting
temperature.
Inventors: |
Wang; Jingdai (Zhejiang,
CN), Wu; Wenqing (Tianjin, CN), Yang;
Yongrong (Zhejiang, CN), Han; Guodong (Tianjin,
CN), Wang; Xiaofei (Tianjin, CN), Cui;
Yuhui (Tianjin, CN), Jiang; Binbo (Zhejiang,
CN), Huang; Zhengliang (Tianjin, CN), Sun;
Jingyuan (Zhejiang, CN), Hu; Xiaobo (Zhejiang,
CN), Fan; Xiaoqiang (Zhejiang, CN), Liao;
Zuwei (Zhejiang, CN), Yang; Yao (Zhejiang,
CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
CHINA PETROLEUM & CHEMICAL CORPORATION
ZHEJIANG UNIVERSITY |
Beijing
Zhejiang |
N/A
N/A |
CN
CN |
|
|
Assignee: |
CHINA PETROLEUM & CHEMICAL
CORPORATION (Beijing, CN)
ZHEJIANG UNIVERSITY (Zhejiang, CN)
|
Appl.
No.: |
16/095,670 |
Filed: |
April 22, 2016 |
PCT
Filed: |
April 22, 2016 |
PCT No.: |
PCT/CN2016/080041 |
371(c)(1),(2),(4) Date: |
October 22, 2018 |
PCT
Pub. No.: |
WO2017/181424 |
PCT
Pub. Date: |
October 26, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190127501 A1 |
May 2, 2019 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F
210/14 (20130101); C08F 2/01 (20130101); C08K
5/01 (20130101); C08F 210/02 (20130101); C08L
23/0815 (20130101); C08F 210/16 (20130101); C08F
2/001 (20130101); C08F 210/16 (20130101); C08F
2/34 (20130101); C08F 2500/12 (20130101); C08L
2203/162 (20130101); C08F 2500/01 (20130101); C08F
110/02 (20130101); C08F 2500/04 (20130101); C08F
2500/08 (20130101); C08F 210/16 (20130101); C08F
210/14 (20130101); C08F 2500/08 (20130101); C08F
2500/12 (20130101); C08F 2500/26 (20130101) |
Current International
Class: |
C08F
210/02 (20060101); C08L 23/08 (20060101); C08F
110/02 (20060101); C08K 5/01 (20060101); C08F
2/01 (20060101); C08F 210/14 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1118361 |
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Mar 1996 |
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CN |
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102307915 |
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Jan 2012 |
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CN |
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103864970 |
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Jun 2014 |
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CN |
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104761788 |
|
Jul 2015 |
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CN |
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105732870 |
|
Jul 2016 |
|
CN |
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2000212341 |
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Aug 2000 |
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JP |
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Other References
JP-2000212341-A, Aug. 2000, Derwent AB. (Year: 2000). cited by
examiner.
|
Primary Examiner: Sastri; Satya B
Attorney, Agent or Firm: Novick, Kim & Lee, PLLC Xue;
Allen
Claims
The invention claimed is:
1. A polyethylene material, having: a density distribution in a
range of 0.880 g/cm.sup.3 to 0.960 g/cm.sup.3; an amount of eluted
fraction at 40.degree. C. in a range of 9.0 wt % to 40.0 wt %, an
amount of eluted fraction at 50.degree. C. in a range of 9.0 wt %
to 40.0 wt %, and an amount of eluted fraction at 60.degree. C. in
a range of 9.9 wt % to 12.4 wt %, as determined by temperature
rising elution fractionation on the polyethylene material; and a
melting temperature of the polyethylene material is in a range of
110.degree. C. to 135.degree. C.
2. The polyethylene material according to claim 1, having an amount
of eluted fraction at a temperature of 110.degree. C. in a range of
8.0 wt % to 30.0 wt %.
3. The polyethylene material according to claim 1, wherein a
standard deviation of eluted fractions of the polyethylene material
40.degree. C., 50.degree. C., 60.degree. C., 70.degree. C.,
80.degree. C., 90.degree. C., 100.degree. C., and 110.degree. C. is
in a range of 0% to 6.0%.
4. The polyethylene material according to claim 1, having a
number-average lamella thickness in a range of 6 nm to 18 nm, a
weight-average lamella thickness in a range of 8 nm to 20 nm, and a
distribution coefficient of the lamella thickness is in a range of
1 to 1.333.
5. The polyethylene material according to claim 1, having a
weight-average molecular weight in a range of 5000 to 350000, and a
molecular weight distribution coefficient in a range of 2.0 to
15.0.
6. The polyethylene material according to claim 1, having: a melt
flow index, at 230.degree. C. and 2.16 kg, in a range of 0.8 g/10
min to 2.0 g/10 min; a tensile yield strength in a range of 15 MPa
to 25 MPa; an elongation at break in a range of 450% to 700%; a
falling dart impact strength in a range of 200 g to 260 g; and/or a
haze in a range of 6% to 18%.
7. The polyethylene material according to claim 1, wherein the
polyethylene material is prepared in a single reactor.
8. The polyethylene material according to claim 7, wherein the
polyethylene material is prepared in the single reactor by
alternately conducting ethylene homopolymerization reaction and
ethylene copolymerization reaction, or by alternately conducting
different copolymerization reactions.
9. A method for preparing the polyethylene material according to
claim 1, comprising: introducing a reaction material containing
ethylene into a single reactor for polymerization reaction; and
intermittently adding a condensate containing a comonomer into the
single reactor so that the polymerization reaction alternates
between ethylene homopolymerization and ethylene copolymerization,
or changes among a plurality of copolymerization reactions in the
single reactor.
10. The method according to claim 9, wherein the polymerization
reaction changes between ethylene homopolymerization and ethylene
copolymerization at least once per hour, and/or the polymerization
reaction changes from a first copolymerization reaction to a second
copolymerization at least once per hour.
11. The method according to claim 9, wherein each
homopolymerization is carried out continuously for 3 min to 60 min,
and each copolymerization reaction is carried out continuously for
5 min to 60 min.
12. The method according to claim 9, wherein the comonomer is
selected from olefins containing less than 18 carbon atoms.
13. The method according to claim 9, wherein the condensate
comprises at least one compound selected from the group consisting
of C.sub.4 to C.sub.7 saturated linear or branched alkanes, and
C.sub.4 to C.sub.7 cycloalkanes.
14. The method according to claim 9, further comprising introducing
at least one ingredient selected from the group consisting of a
promoter, an antistatic agent, a chain transfer agent, a molecular
regulator, a condensing agent, and an inert gas into the single
reactor.
15. The method according to claim 9, wherein the polymerization
reaction is carried out at a pressure of 0.5 MPa to 10 MPa and a
temperature of 40.degree. C. to 150.degree. C.
16. The polyethylene material according to claim 1, wherein the
polyethylene material is a copolymer of ethylene/1-hexene, a random
copolymer of ethylene/1-butene/1-hexene, or a random copolymer of
ethylene/1-hexene/1-octene.
17. A polymeric film comprising the polyethylene material according
to 1.
18. The polyethylene material according to claim 1, having an
amount of eluted fraction at 40.degree. C. in a range of 10.0 wt %
to 25.0 wt % and a melting temperature in a range of 116.degree. C.
to 130.degree. C.
19. The polyethylene material according to claim 1, having an
amount of eluted fraction at 40.degree. C. in a range of 9.9 wt %
to 20.0 wt %, and an amount of eluted fraction at 110.degree. C. in
a range of 9.0 wt % to 18.0 wt %.
20. The polyethylene material according to claim 1, wherein a
standard deviation in amounts of two eluted fractions, measured
from 40.degree. C. to 110.degree. C. at an interval of 10.degree.
C., is in the range of 0.5% to 3.5%.
21. The polyethylene material according to claim 1, having a
weight-average molecular weight in a range of 10000 to 250000 and a
molecular weight distribution coefficient in a range of 2.5 to
6.0.
22. The polyethylene material according to claim 1, wherein the
polyethylene material is prepared in a fluidized bed reactor.
23. The polyethylene material according to claim 8, wherein the
polyethylene material is prepared by first conducting ethylene
copolymerization reaction, and then alternately conducting ethylene
homopolymerization reaction and ethylene copolymerization reaction
or alternately conducting different copolymerization reactions.
24. The method according to claim 9, wherein the polymerization
reaction changes between ethylene homopolymerization and ethylene
copolymerization three times or more per hour, and/or the
polymerization reaction changes amongst three or more different
copolymerization reactions.
25. The method according to claim 9, wherein each
homopolymerization is carried out continuously for 8 min to 20 min,
and each copolymerization reaction is carried out continuously for
8 min to 20 min.
26. The method according to claim 9, wherein the comonomer is
selected from butene, hexene, and octene.
27. The method according to claim 9, wherein the condensate
comprises at least one compound selected from n-pentane,
isopentane, hexane, and heptanes.
28. The method according to claim 9, wherein the polymerization
reaction in the reactor is carried out at a pressure of 1.5 MPa to
5 MPa and at a temperature of 50.degree. C. to 120.degree. C.
29. The film according to claim 17, wherein the film is a
retortable film, a high-transparency film, a barrier and protective
film, a heat-seal film, a tag film, or a medical package film.
Description
FIELD OF THE INVENTION
The present application relates to the technical field of
polyethylene, and in particular to a new polyethylene polymer and
application thereof.
BACKGROUND OF THE INVENTION
Currently, polyethylene is the most widely used and most produced
olefin polymer. It is a general-purpose thermoplastic with various
structures and properties, and is one of the primary types of
synthetic resins. Polyethylene can be classified into many types.
There are, for example, high-density polyethylene (HDPE, having a
density of 0.940 g/cm.sup.3-0.960 g/cm.sup.3), medium-density
polyethylene (MDPE, having a density of 0.926 g/cm.sup.3-0.940
g/cm.sup.3), low-density polyethylene (LDPE, having a density of
0.88 g/cm.sup.3-0.926 g/cm.sup.3), linear low-density polyethylene
(LLDPE, having a density of 0.915 g/cm.sup.3-0.926 g/cm.sup.3), and
very-low-density polyethylene (VLDPE, having a density of 0.890
g/cm.sup.3-0.915 g/cm.sup.3). Polymerization processes for
producing polyethylene mainly include: slurry polymerization,
solution polymerization, and gas phase polymerization, among which
gas phase polymerization in fluidized bed reactors is capable of
producing about 1/3 of the world's total polyethylene, and
producing nearly 1/2 of the total polyethylene in China. Compared
with other polymerization processes, the gas phase polymerization
has advantages of being simple, short, and flexible, being operable
under moderate conditions, and being capable of realizing easy
solvent recovery and easy grade transition (i.e. grade switch-over
of polyethylene product).
Molecular weight and molecular weight distribution of polyethylene
have great influences on properties of polyethylene.
High-molecular-weight polyethylene has good physical mechanical
properties, but is not easy to process. Low-molecular-weight
polyethylene exhibits good rheological properties when being
processed, but physical mechanical properties thereof are poor. In
the past, a commonly used method for regulating the molecular
weight and molecular weight distribution of polyethylene is to
change the partial pressure of hydrogen in a reaction system.
Nowadays the regulation of polyethylene production is no longer
limited to this method. The addition of an .alpha.-olefin comonomer
can also change the molecular weight and molecular weight
distribution of polyethylene. Meanwhile, the .alpha.-olefin
comonomer can change structures of side chains of polyethylene, and
can therefore regulate the physical property and machinability of
polyethylene.
European patent EP 0038119 relates to a terpolymer of propylene,
ethylene and another .alpha.-olefin, the total amount of ethylene
and .alpha.-olefin in the terpolymer being in the range set by the
following equation: ethylene % by weight+A. .alpha.-olefin % by
weight=3.0% to 5.0% by weight, wherein when the .alpha.-olefin is
hexene-1, A is 0.455. Terpolymers with properties falling outside
this range are suitable for producing films. Patent application
WO2006/002778 relates to pipe systems made from copolymers of
propylene/ethylene, and .alpha.-olefins, wherein the amount of
ethylene ranges from 0% to 9% by moles, preferably from 1% to 7% by
moles, and the amount of hexene-1 ranges from 0.2% to 5% by moles.
When the amounts of ethylene and hexene-1 are selected from these
ranges, a polymer with improved properties suitable for use of
films can be obtained.
Chinese patent CN1384844 relates to copolymers of ethylene with
C.sub.3-C.sub.12 .alpha.-olefins. The copolymers have a molecular
weight distribution Mw/Mn of <10, a density of 0.85 g/cm.sup.3
to 0.95 g/cm.sup.3, a proportion of 1 to 40% by weight and a molar
mass Mn of more than 150000 g/mol and the breadth index of the
composition distribution of the comonomer is more than 70%. The
polymers can be used for fibers, molded articles, films or polymer
mixtures.
Although the synthesis process of ethylene copolymers by using
.alpha.-olefins as comonomers has produced various types of
polyethylene, there are still many countries throughout the world
which do not have and are not capable of having the equipment for
large-scale production of ethylene/.alpha.-olefin copolymers. A
type of polyethylene with excellent properties is therefore still
desirable in current and future market especially in regions
lacking .alpha.-olefin resources. More importantly, there is still
an increasing demand for a type of polyethylene with special
structure and composition characteristics. It is therefore of great
significance to reinforce the research and development of
olefin-copolymerized polyethylene products.
SUMMARY OF THE INVENTION
One of the objectives of the present application is to provide a
new type of polyethylene polymer which can be prepared in a single
reactor by alternately conducting olefin copolymerization and
olefin homopolymerization. The new type of polyethylene polymer may
be a polyethylene product covering all densities of polyethylene
from very-low-density polyethylene (VLDPF) to high-density
polyethylene (HDPE). Low-molecular-weight fractions of the
polyethylene are large in amount and are highly branched, and the
polyethylene has very good physical properties such as good
malleability.
The present application provides a polyethylene material. A density
distribution of the polyethylene material is in a range of 0.880
g/cm.sup.3-0.960 g/cm.sup.3. An amount of a fraction at a
temperature of 40.degree. C., as determined by conducting
temperature rising elution fractionation on the polyethylene
material, is in a range of 9.0 wt %-40.0 wt %, preferably in a
range of 10.0 wt %-25.0 wt %, more preferably in a range of 9.9 wt
%-20.0 wt %. A melting temperature of the polyethylene material is
in a range of 110.degree. C.-135.degree. C., preferably in a range
of 116.degree. C.-130.degree. C., more preferably in a range of
119.degree. C.-128.degree. C.
The amount of the fraction at 40.degree. C. is for example 9.0 wt
%, 9.5 wt %, 9.9 wt %, 10.0 wt %, 11.0 wt %, 12.0 wt %, 13.0 wt %,
14.0 wt %, 15.0 wt %, 16.0 wt %, 18.0 wt %, 20.0 wt %, 22.0 wt %,
or 24.0 wt %.
The melting temperature of the polyethylene material is for
example, 116.degree. C., 118.degree. C., 120.degree. C.,
121.degree. C., 122.degree. C., 123.degree. C., 125.degree. C., or
128.degree. C.
In a preferred embodiment of the present application, the amount of
the fraction of the polyethylene material at 50.degree. C. is in a
range of 9.0 wt %-40.0 wt %, preferably in a range of 10.0 wt
%-25.0 wt %, more preferably in a range of 10.2 wt %-16.0 wt %, for
example 9.5 wt %, 9.9 wt %, 10.2 wt %, 11.0 wt %, 12.0 wt %, 13.0
wt %, 14.0 wt %, or 15.0 wt %.
A prominent feature of the polyethylene polymer provided by the
present application is that compared with existing routine
polyethylene for example the polyethylene prepared by the
traditional gaseous polymerization, it has distinctly improved
amount of low-molecular-weight fractions (especially the fraction
at 40.degree. C.) and the low-molecular-weight fractions are highly
branched. It is known that the smaller the molecular weight of
polyethylene is, the higher the branching degree is, and the lower
the crystallinity degree is. Therefore, it can be appreciated by
those skilled in the art that when the amount of
low-molecular-weight fractions is high, the melting temperature of
the polyethylene material will decrease. However, the inventors of
the present application were surprised to find that the
polyethylene material provided by the present application still has
a relatively high melting temperature despite that the amount of
its low-molecular-weight fractions was high. The inventors further
found that the polyethylene material of the present application and
having such a feature has excellent bidirectional malleability and
is a material having good machinability and applicability
especially suitable for use in preparation of films.
In a preferred embodiment of the present application, an amount of
a fraction of the polyethylene material at 110.degree. C. is in a
range of 8.0 wt %-30.0 wt %, preferably in a range of 9.0 wt %-18.0
wt %, for example 9.0 wt %, 10.0 wt %, 11.0 wt %, 12.0 wt %, 13.0
wt %, 14.0 wt %, 15.0 wt %, or 16.0 wt %.
The amount of high-molecular-weight fractions (especially fractions
at 110.degree. C.) of the polyethylene material provided by the
present application is also relatively high, and the branching
degree thereof is also improved compared with commonly used
polyethylene. Therefore, branches in the polyethylene polymer
provided by the present application are widely distributed among
molecular chains, and many branches are distributed in
high-molecular-weight fractions.
In a preferred embodiment of the present application, as determined
by temperature rising elution fractionation, a standard deviation
of amounts of two fractions of the polyethylene material at
temperatures at an interval of 10.degree. C. from 40.degree. C. to
110.degree. C. is in a range of 0%-6.0%, preferably in a range of
0.5%-3.5%. According to this preferred embodiment of the present
application, the amounts of different fractions of the polyethylene
material are relatively average. This also reflects that the amount
of the high-molecular-weight fractions and the amount of
low-molecular-weight fractions of the polyethylene material of the
present application are relatively high.
In a preferred embodiment of the present application, a
number-average lamella thickness of the polyethylene material is in
a range of 6 nm-18 nm, and a weight-average lamella thickness
thereof is in a range of 8 nm-20 nm; a distribution coefficient of
the lamella thickness (the weight-average lamella
thickness/number-average lamella thickness) is preferably in a
range of 1-1.333. The lamella thickness may be measured by the
thermal fractionation by successive self-nucleation/annealing (SSA)
technique which is commonly known in the art.
In a preferred embodiment of the present application, a
weight-average molecular weight of the polyethylene material is in
a range of 5000-350000, preferably in a range of 10000-250000, and
a molecular weight distribution coefficient is in a range of
2.0-15.0, preferably in a range of 2.5-6.0.
According to a preferred embodiment of the present application, a
melt flow index (230.degree. C., 2.16 kg) of the polyethylene
material is in a range of 0.8 g/10 min-2.0 g/10 min; a tensile
yield strength thereof is in a range of 15 MPa-25 MPa; an
elongation at break thereof is in a range of 450%-700%; and/or a
falling dart impact strength thereof is in a range of 200 g-260 g.
The haze of the polyethylene material provided by the present
application is preferably in a range of 6%-18%.
The polyethylene material provided by the present application thus
has good malleability and other good mechanical properties.
As can be seen from the foregoing, the present application provides
a new polyethylene material having the above unique features (or
combinations of features) and having good mechanical properties and
machinability.
In a preferred embodiment of the present application, the
polyethylene material is prepared in a single reactor.
In a more preferred embodiment of the present application, the
polyethylene material is prepared in the single reactor by
alternately conducting ethylene homopolymerization reaction and
ethylene copolymerization reaction, or by alternately conducting
different copolymerization reactions.
In other words, the polyethylene material provided by the present
application is not prepared by physical mixing of ethylene
homopolymers and/or ethylene copolymers having different molecular
weights, or prepared by mixing and melting of the these components.
Instead, the polyethylene material provided by the present
application is prepared by chemical mixing of different fractions,
i.e. mixing of different molecular chains.
In a preferred embodiment of the present application, the
polyethylene material is prepared by a method (gas and liquid
olefin polymerization process) comprising steps of: introducing a
reaction material containing ethylene into the single reactor for
polymerization reaction; and intermittently adding a condensate
containing a comonomer so as to control and realize switching
between ethylene homopolymerization and copolymerization, or
switching between different copolymerization reactions in the
single reactor.
To add the condensate containing the comonomer or not may be
decided based on the predetermined type of the reaction to be
carried out in the reactor, i.e., whether the reaction in the
reactor is ethylene copolymerization or homopolymerization. For
example, if it is determined that the reaction to be carried out
next is a homopolymerization reaction, then the comonomer is not
added any more. On the contrary, if it is determined that the
reaction to be carried out next is a copolymerization reaction,
then it is necessary to choose and introduce a suitable comonomer
as required. Therefore, the expression "intermittently adding a
condensate" means "to selectively add the condensate", for example,
"to add the condensate every once in a while" or "not to add the
condensate every once in a while", depending on requirement for the
type of the reaction (copolymerization, or homopolymerization) to
be carried out in the reactor.
In a preferred embodiment of the present application, condensates
containing different types of comonomers may be stored separately
in different storage tanks, and introduced into the reactor as
required at a proper time.
In a preferred embodiment of the present application, preferably,
ethylene copolymerization reaction is first carried out, and then
ethylene homopolymerization reaction and ethylene copolymerization
reaction are alternately carried out or different copolymerization
reactions are alternately carried out. In other words, the initial
reaction is ethylene copolymerization, and then the reaction is
switched to ethylene homopolymerization, and after that the
reaction is continued based on a predetermined reaction switching
program. This preferred embodiment is advantageous in that
copolymerization polyethylene particles produced in the initial
reaction are loose, and active centers in the particles will not be
buries, which ensures subsequent polymerization activity.
In a preferred embodiment of the present application, the
polymerization reaction in the reactor is carried out at a pressure
of 0.5 MPa-10 MPa, preferably 1.5 MPa-5 MPa, and at a temperature
of 40.degree. C.-150.degree. C., preferably 50.degree.
C.-120.degree. C.
In a specific example, when ethylene homopolymerization is carried
out, the gas material is discharged out of the reactor through its
top outlet, and is then compressed, condensed, and subjected to
gas-liquid separation to generate a gas material flow and a liquid
material flow. The liquid material flow mainly contains a comonomer
and a condensate, and can be stored in a storage tank. The gas
material flow mainly contains ethylene and hydrogen, and it is
circulated, together with other materials, into the reactor through
the bottom of the fluidized bed reactor. At this time, the inside
of fluidized bed reactor is primarily an atmosphere of ethylene and
hydrogen and contains little comonomer and condensate. In this
case, growth polymerization of oethylene and homopolymerization
occurs, and low-branching and high-density HDPE is thus produced.
After the polymerization reaction proceeded for the predetermined
time, the reaction is switched to ethylene copolymerization. The
comonomer and the condensate are introduced into the reactor from
the storage tank. The comonomer and the condensate may be
introduced into the reactor from the bottom of the reactor or from
a side wall of the upper part of the distribution plate through one
inlet or through multiple inlets. Low-density and
high-molecular-weight polyethylene is generated at a
low-temperature reaction zone located at the lower portion;
high-density and low-molecular-weight polyethylene is generated at
a high-temperature reaction zone at the upper portion. Unreacted
materials are discharged out of the reactor from its top and is
compressed, condensed, and subjected to gas-liquid separation. The
gas material flow and the liquid material flow resulted from the
gas-liquid separation are all circulated back to the fluidized bed
for continued reaction. When the reaction is finished after a
predetermined polymerization time, the reaction is switched to
olefin homopolymerization. Such operations are carried out
sequentially and alternately. The total time for the polymerization
is preferably 2 hs to 4 hrs. A polyethylene of excellent properties
as desired is finally produced.
When ethylene copolymerization is used to prepare low/high-density
polyethylene, the reaction system is supplied with ethylene, a
comonomer, hydrogen, a catalyst, a promoter, and a condensing
agent. The reactor is provided therein with a gas-liquid-solid
reaction zone and a gas-solid reaction zone. The gas-solid reaction
zone is a high-temperature reaction zone which contains a small
amount of the comonomer, and the temperature thereof is preferably
in a range of 80.degree. C.-110.degree. C., more preferably in a
range of 80.degree. C.-104.degree. C. The polyethylene generated in
this reaction zone has a relatively high density and a relatively
low molecular weight. The gas-liquid-solid reaction zone is a
low-temperature reaction zone which contains a large amount of the
comonomer, and the temperature thereof is preferably in a range of
50.degree. C.-77.degree. C., more preferably in a range of
60.degree. C.-77.degree. C. The polyethylene generated in this
reaction zone has a relatively low density and a relatively high
molecular weight.
Further preferably, a temperature difference of at least 10.degree.
C., preferably of at least 15.degree. C., exists between the
gas-solid reaction zone and the gas-liquid-solid reaction zone.
In a preferred embodiment, at ethylene homopolymerization stage,
the polymerization temperature is in a range of 80.degree.
C.-110.degree. C., preferably in a range of 85.degree.
C.-110.degree. C.
In a preferred embodiment of the present application, the switching
between ethylene homopolymerization and the copolymerization is
performed once per hour, preferably three times or more than three
times per hour.
In a preferred embodiment of the present application, the switching
between the different copolymerization reactions is performed at
least once per hour, preferably three times or more than three
times per hour.
According to a preferred embodiment of the present application,
each homopolymerization is carried out continuously for 3 min-60
min, preferably 8 min-20 min; and each copolymerization reaction is
carried out continuously for 5 min-60 min, preferably 8 min-20
min.
In a preferred embodiment of the present application, in ethylene
copolymerization, the mole ratio of the comonomer to ethylene in
the reactor is in a range of 0-0.1.
In a preferred embodiment of the present application, in olefin
homopolymerization and olefin copolymerization, the mole ratio of
the hydrogen to ethylene in the reactor is in a range of
0.01-1.0.
In a preferred embodiment of the present application, a flow rate
of the reaction material gas is 1 ton/hr-500 ton/hr.
According to a preferred embodiment of the present application, the
comonomer is selected from olefins containing less than 18 carbon
atoms, preferably selected from the group consisting of butene,
hexene, and octene, especially preferably selected from the group
consisting of .alpha.-butene, .alpha.-hexene, and .alpha.-octene,
most preferably is 1-hexene. The polyethylene material provided by
the present application is preferably at least one random copolymer
of ethylene and butene, and hexene and octene.
According to a preferred embodiment of the present application, the
polyethylene material is a copolymer of ethylene/1-hexene, a random
copolymer of ethylene/1-butene/1-hexene, or a random copolymer of
ethylene/1-hexene/1-octene.
In a specific example of the present application, the polyethylene
material is a copolymer of ethylene/1-butene/1-hexene, which is
prepared by first carrying out a copolymerization reaction of
ethylene, 1-butene, and 1-hexene, then switching to ethylene
homopolymerization, again switching to copolymerization reaction of
ethylene, 1-butene, and 1-hexene, and repeating these reactions
alternately. The time for the copolymerization and
homopolymerization reactions is defined as above.
In a specific example of the present application, the polyethylene
material is a copolymer of ethylene/1-hexene/1-octene, which is
prepared by first carrying out a copolymerization reaction of
ethylene and 1-octene, then switching to ethylene
homopolymerization, then switching to copolymerization reaction of
ethylene and 1-hexene, then switching to ethylene
homopolymerization, and again switching to copolymerization
reaction of ethylene and 1-octene, and repeating these reactions
alternately. The time for the copolymerization and
homopolymerization reactions is defined as above.
A suitable condensate comprises at least one selected from the
group consisting of C4-C7 saturated linear or branched alkanes, and
C4-C7 cycloalkanes, preferably at least one selected from the group
consisting of n-pentane, isopentane, hexane, and heptanes, most
preferably is isopentane and/or hexane.
According to a preferred embodiment of the present application, in
process of the polymerization reaction, at least one selected from
the group consisting of a promoter, an antistatic agent, a chain
transfer agent, a molecular regulator, a condensing agent, and an
inert gas, is introduced into the reactor. The condensing agent in
this preferred embodiment is an additional condensing agent, namely
a condensing agent that may not contain comonomer.
The antistatic agent is a commonly used antistatic agent, which is,
for example, one selected from the group consisting of aluminium
distearate, ethoxylated amine, polysulfone copolymer, polymerized
polyamine, oil soluble sulfoacid, and compositions comprising
several of the foregoing.
The chain transfer agent is a commonly used chain transfer agent,
which comprises hydrogen and a metal alkyl, preferably is
hydrogen.
The inert gas may be a commonly used inert gas such as
nitrogen.
The catalyst used in the preparation of the polyethylene material
of the present application may be at least one of the following:
Ziegler-Natta catalyst, a metallocene catalyst, a transition metal
catalyst, inorganic chromium catalyst, organic chromium catalyst,
or a composite catalyst comprising two catalysts. The catalyst is
preferably a titanocene catalyst capable of enabling polymerization
of polyethylene, more preferably a titanocene catalyst capable of
loading on a carrier. The promoter is at least one selected from
the group consisting of modified aluminoxane, aluminium diethyl
monochloride, aluminium diisobutyl monochloride, ethylaluminum
sesquichloride, aluminium diisobutyl, aluminium ethyl dichloride,
trimethylaluminum, aluminumtriethyl, triisobutyl aluminium,
trioctylaluminum, aluminium diethyl monohydrogen, and aluminium
diisobutyl monohydrogen, and is preferably aluminumtriethyl or
triisobutyl aluminium.
According to the present application, the reactor used for
preparing the polyethylene material of the present application is
preferably a fluidized bed reactor.
The present application further provides use of the polyethylene
material of the present application, for example in preparation of
films. The films (film products) preferably comprise package
materials and/or product tags, more preferably comprising
retortable films, high-transparency films, barrier and protective
films, heat-seal films, tag films, or medical package films.
The polyethylene material provided by the present application has
unique features. For example, the amount of low-molecular-weight
and high-branching fractions is high, and the amount of
high-molecular-weight fractions in also relatively high. Besides,
the high-molecular-weight fractions are highly branched. Further,
the polyethylene material is a polyethylene product covering all
densities of polyethylene, and has suitable molecular weight and
molecular weight distribution. The polyethylene material provided
by the present application therefore has improved mechanical
properties and processability such as good machinability and impact
resistance, and is a material having promising application
prospect.
BRIEF DESCRIPTION OF THE DRAWINGS
The present application will be described below in detail with
reference to the accompanying drawings. It shall be appreciated
that the drawings are provided merely for a better understanding of
the present application, and shall not be construed as limiting the
present application.
FIG. 1 shows results of comparison between branching analysis of
polyethylene prepared in example 1 and branching analysis of
polyethylene prepared in comparative example 3.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The present application will be explained below in detail with
reference to the examples and the accompanying drawings. It shall
be appreciated that the examples and the drawings are merely
exemplary descriptions of the present application, and shall not be
construed as limiting protection scope of the present application.
All reasonable variations and combinations within the spirit of the
present application shall fall within the protection scope of the
present application.
The characteristic parameters mentioned in the present application
were determined by way of the methods described below.
Melting Temperature: A differential scanning calorimeter (Model: TA
Q200; from TA Instruments, USA) was used to measure a melting
temperature. The method for the measurement was specifically as
follows. A sample of about 6 mg was first weighed. The sample was
heated to a temperature of 220.degree. C. at a rate of 20.degree.
C./min and then kept in a nitrogen gas flow for 2 min. Then the
sample was cooled to a temperature of about 40.degree. C. at a rate
of 20.degree. C./min and kept at 40.degree. C. for 2 min for its
crystallization. After that, the sample was heated to a temperature
of 220.degree. C. at a rate of 20.degree. C./min for melting again.
The process of melting and scanning were recorded to obtain a
thermogram. A melting temperature was read from the thermogram.
Melt Flow Rate (MFR): MFR was determined according to GB/T3682-83
at a temperature of 230.degree. C. under a load of 2.16 kg.
Density: Density was determined according to GB/T1033-70.
Tensile Yield Strength and Elongation at Break: Tensile yield
strength and elongation at break were measured according to
GB/T1040-79.
Haze: Haze was determined according to GB/T2410-80.
Falling Dart Impact Strength: Falling dart impact strength was
determined according to GB/T9639-88.
Weight-average Molecular Weight and Molecular Weight Distribution
Coefficient: Weight-average molecular weight and molecular weight
distribution coefficient were determined by using Gel Permeation
Chromatography with Polymer Laboratories PL-220. Column and rotary
chamber were operated at a temperature of 140.degree. C.
1,2,4-trichlorobenzene was used as a solvent. The concentration of
the polymer is 3.Salinity.. The volume of the injection was 100
.mu.L. The flow rate was 1.0 mL/min.
Temperature Rising Elution Fractionation (TREF) Experiment
TREF technique, taking advantage of the principle that different
chain structure parameters have different influences on the
crystallization and crystallinity of polyethylene, separates
polyethylene molecules on the basis of crystallinity into multiple
narrowly distributed fractions.
The process of TREF includes two stages: crystal precipitation and
temperature rising elution.
At the crystal precipitation stage, polyethylene is dissolved at a
high temperature to form a stable and dilute solution, and then the
temperature is slowly lowered so that polyethylene crystal
precipitated on a surface of a carrier substance (for example inert
particulates such as quartz sand). Polyethylene molecules with
different chain structures then form a crystal layer with gradient
degrees of crystallinity. For example, polyethylene molecules with
different contents of short-chain branches, due to their different
crystallizability, would form a gradient distribution from inside
to outside based on degrees of crystallinity.
At the temperature rising elution stage, the carrier substance with
polyethylene crystal layer precipitated thereon is loaded in an
elution column. Then, under the condition of continuous or intermit
temperature rising, a good solvent of polyethylene is used to elute
the carrier substance. Polyethylene products with different degrees
of crystallinity are thus separated.
The TREF experiment used in the present application was a common
operation in the art, and it was carried out specifically as
follows.
(1) Treatment of Quartz Sand
Quartz sand was filled into an elution bottle, and washed with
water to remove impurities. 50 mesh quartz sand was selected. The
washed quartz sand was then roasted for 4 hours at a temperature of
800.degree. C. After that, the elution bottle was filled with the
treated quartz sand to a given height.
(2) Preparation of Polymer Solution
1.2 g of polymer sample (with the addition of 0.1 g of antioxidant
BHT) was dissolved into 250 ml of xylene contained in a magnetic
stirring vessel. After solids were dissolved in the solution and
were no longer visible to naked eyes, the solution was stirred
continuously for 2 hours to ensure adequate dissolution of the
polymer sample. After that, the dissolved sample was carefully and
rapidly poured into the quartz sand-containing bottle through a
narrow neck of a three-neck flask, and was then washed with 60 ml
of xylene solution which was poured into the quartz sand-containing
elution bottle at two different times. It should be ensured that a
surface of the entire solution after washing is lower than a
surface of the quartz sand, preferably lower than the surface of
the quartz sand by 1 cm to 2 cm.
(3) Programmed Cooling (Crystal Precipitation Stage)
After the sample solution was introduced into the elution bottle,
programmed cooling of an oil bath was initiated. The temperature
was lowered from 130.degree. C. to room temperature (30.degree. C.)
at a rate of 1.5.degree. C./h. During this process, polymers with a
high-crystallization-temperature were first precipitated and
covered the surface of the quartz sand, and then polymers with a
low-crystallization-temperature were precipitated.
(4) Programmed Temperature Rising (Temperature Rising Elution
Stage)
A flask containing pure xylene solvent was placed in an oil bath
controlled by programmed temperature rising. Xylene was then
introduced into the elution bottle through the high-end with a
circulating pump, and the polymer solutions at different elution
temperatures were pumped into collection flasks by means of a
liquid level difference. The present application collected and
measured fraction eluents in an elution temperature range of
40.degree. C. to 110.degree. C., and theeluent sample of a
corresponding fraction was collected every 10.degree. C.
(5) Treatment of Elution Solution
The obtained eluents of various fractions were vacuum concentrated
by a rotary evaporator, respectively. Then, they were respectively
precipitated by using isopropanol, then filtered, roasted, weighed,
and finally calculated a content thereof.
Thermal Fractionation by Successive Self-Nucleation/Annealing (SSA)
Experiment
SSA thermal fractionation technique usually includes the following
steps.
(1) A sample is heated to a temperature higher than its melting
temperature (at least 25.degree. C. higher than the melting
temperature), and then kept at the temperature for a time so as to
eliminate heat history.
(2) The sample is cooled at a certain temperature-decreasing rate
to a predetermined lowest temperature (this lowest temperature
ensures that the sample can be crystallized at this temperature),
and then kept at the lowest temperature for a time.
(3) The sample is heated at a certain temperature-increasing rate
to a first predetermined self-nucleation temperature T.sub.s (which
is usually 25.degree. C. higher than the melting temperature), and
then kept at the temperature for a time.
(4) Step (2) is repeated.
(5) The sample is heated at a certain temperature-increasing rate
to a second predetermined self-nucleation temperature T.sub.s
(which is lower than the first predetermined self-nucleation
temperature T.sub.s by 2.5.degree. C. or 5.degree. C.), and then
kept at the temperature for a time; heating is run repeatedly (the
temperature range of the whole thermal fractionation treatment is
similar to the melting range of the sample).
(6) The sample is heated at a certain temperature-increasing rate
to the melting temperature set in step (1), and a temperature
rising melting curve is recorded.
The thermal fractionation by SSA technique adopted in the present
application is a common operation in the art, and it is
specifically as follows.
A differential scanning calorimeter (Model: TA Q200; from TA
Instruments, USA) was used. In a nitrogen atmosphere, a
polyethylene sample was heated at a rate of 10.degree. C./min from
room temperature to 160.degree. C. and kept at 160.degree. C. for 3
min to eliminate heat history; the polyethylene sample was then
cooled at a rate of 10.degree. C./min to 0.degree. C. and kept at
0.degree. C. for 5 min; the sample was again heated at a rate of
10.degree. C./min to a nucleation temperature T.sub.s and kept at
the nucleation temperature T.sub.s for 5 min; the sample was again
cooled at a rate of 10.degree. C./min to 0.degree. C. and kept for
5 min. A self-nucleation process was thus completed. The
fractionation results of the self-nucleation and annealing of
polyethylene at temperatures of 127.degree. C., 122.degree. C.,
117.degree. C., 112.degree. C., 107.degree. C., 102.degree. C., and
97.degree. C. were recorded, and fractions at each of the forgoing
temperatures were expressed in sequence as P1, P2, P3, P4, P5, P6,
P7. After the fractionation, the sample was heated at a rate of
10.degree. C./min to 160.degree. C., and a final melting curve was
recorded.
EXAMPLE 1
Ethylene homopolymerization and ethylene/1-hexene copolymerization
were carried out in a fluidized bed reactor to prepare the
polyethylene material of the present application. The fluidized bed
reactor was filled with a catalyst system of Ziegler-Natta catalyst
and triethylaluminum. A reaction material gas (containing nitrogen,
hydrogen, ethylene, methane, ethane, 1-hexene, and a small amount
of isopentane) and a condensate isopentane (containing 1-hexene)
were introduced into the reactor through its bottom inlet where the
temperature was 58.degree. C., and ethylene/1-hexene
copolymerization reaction was first carried out. The rest gas after
the reaction was used as a circulating gas and was discharged out
of the reactor through its top outlet. The circulating gas was then
compressed, condensed, and subjected to gas-liquid separation. The
liquid material flow resulted from the gas-liquid separation was
stored in a 1-hexene storage tank, and meanwhile the gas resulted
from the gas-liquid separation was used as circulating gas and was
circulated into the reactor through a reactor feed inlet for
continued reaction. When the circulating gas was introduced into
the bottom portion of the reactor bed, it was a mixture of gas and
liquid. The liquid in the fluidized bed had a mass fraction of 24
wt %, and a superficial fluidizing gas velocity was 0.63 m/s. A
polymerization temperature at the bottom portion of the bed
(gas-liquid-solid reaction zone) was 68.degree. C., while a
polymerization temperature at the top portion of the bed (gas-solid
reaction zone) was 85.degree. C. In the circulating gas, the dew
point temperature of liquid isopentane was between the temperature
of the bottom portion and the temperature of the top portion of the
bed. The copolymerization proceeded for 15 min.
After the copolymerization polymerization reaction proceeded for
the predetermined time, the reaction was switched to ethylene
homopolymerization phase. The circulating gas introduced into the
bottom inlet of the reactor contained hydrogen, nitrogen, methane,
ethane, ethylene, 1-hexene, and a small amount of isopentane, and
had a pressure of 3.1 MPa and a temperature of 100.degree. C. After
the circulating gas was circulated for multiple times, the
circulating gas discharged from a heat exchange did not contain the
condensate, and had a gas density of 28.0 kg/m.sup.3. After
gas-liquid separation, .alpha.-olefin and isopentane (accounting
for 80% of the circulating gas flow) were introduced into a
material storage tank, and a small amount of the condensate and
.alpha.-olefin that did not go through gas-liquid separation was
introduced, together with the circulating gas, into the fluidized
bed reactor. The gaseous polymerization ran for 8 min (including
the operation time for process switching).
Then, the reaction was switched from ethylene homopolymerization to
ethylene/1-hexene copolymerization. A condensate comprising
1-hexene and isopentane was introduced through a feed pump into the
reactor from the upper portion of the distribution plate of the
reactor bed. The polymerization temperature at the lower portion
gradually decreased to 68.degree. C. The copolymerization reaction
at this stage proceeded for 15 min.
The above operations were carried out sequentially and alternately
and the total time of polymerization was carried out for 3 hours.
Polyethylene (a) was thus obtained.
Polyethylene (a) was subjected to temperature rising elution
fractionation testing, successive self-nucleation/annealing (SSA)
thermal fractionation testing, and other property testing,
respectively. The amounts of fractions at different temperatures
were shown in Table 1. Results of thermal fractionation by
successive self-nucleation/annealing (SSA) testing were shown in
Table 2, and results of other property testing were shown in Table
3.
In addition, a nuclear magnetic resonance spectrometer (from
Varian, USA; Model: NMK/300 MHZ) was used to analyze the degree of
branching of polyethylene (a). The analysis results were compared
with the testing results of traditional vapor deposition for
preparing polyethylene. Results were shown in Table 1.
By referring to Table 2 and by introducing parameters of
statistics, polydispersity of lamella thickness was expressed
quantitatively. Equation (1) and equation (2) were used to
respectively calculate the number-average lamella thickness (ln)
and weight-average lamella thickness (lw). Equation (3) was used to
calculate the distribution coefficient (I) of the lamella
thickness. Results were shown in Table 4. The larger I was, the
wider the distribution of the lamella thickness was, i.e., the
wider the crystallizable sequence length distribution was and in a
molecular structure more irregular short-chain branching
distribution was. l.sub.n=(n.sub.1l.sub.1+n.sub.2l.sub.2+ . . .
+n.sub.il.sub.i)/(n.sub.1+n.sub.2+ . . .
+n.sub.i)=.SIGMA.f.sub.il.sub.i (1)
l.sub.w=(n.sub.1l.sub.1.sup.2+n.sub.2l.sub.2.sup.2+ . . .
+n.sub.il.sub.i.sup.2)/(n.sub.1l.sub.1+n.sub.2l.sub.2+ . . .
+n.sub.il.sub.i)=.SIGMA.f.sub.il.sub.i.sup.2/.SIGMA.f.sub.il.sub.i
(2) I=l.sub.w/l.sub.n (3)
In the equations, n.sub.i represents the peak area of each
fraction; l.sub.i, represents the number-average lamella thickness
of each fraction; and f.sub.i represents the relative amount of
each fraction.
EXAMPLE 2
Ethylene homopolymerization and ethylene/1-hexene copolymerization
were carried out in a fluidized bed reactor to prepare the
polyethylene material of the present application. The fluidized bed
reactor was filled with a catalyst system of Ziegler-Natta catalyst
and triethylaluminum. A reaction material gas (containing hydrogen,
nitrogen, methane, ethane, ethylene, 1-hexene, and a small amount
of isopentane) and a condensate isopentane (containing 1-hexene)
were introduced into the reactor through its bottom inlet where the
temperature was 60.degree. C., and ethylene/1-hexene
copolymerization reaction was first carried out. The rest gas after
the reaction was used as a circulating gas and was discharged out
of the reactor through its top outlet. The circulating gas was then
compressed, condensed, and subjected to gas-liquid separation. The
liquid material flow resulted from gas-liquid separation was stored
in a 1-hexene storage tank, and meanwhile the gas resulted from
gas-liquid separation was used as a circulating gas and was
circulated into the reactor through a reactor feed inlet for
continued reaction. When the circulating gas was introduced into
the bottom portion of the reactor bed, it was a mixture of gas and
liquid. The liquid in the fluidized bed had a mass fraction of 26
wt %, and a superficial fluidizing gas velocity was 0.68 m/s. A
polymerization temperature at the bottom portion of the bed
(gas-liquid-solid reaction zone) was 75.degree. C., while a
polymerization temperature at the top portion of the bed (gas-solid
reaction zone) was 92.degree. C. In the circulating gas, the dew
point temperature of liquid isopentane was between the temperature
of the bottom portion and the temperature of the top portion of the
bed. The copolymerization proceeded for 20 min.
After the copolymerization polymerization reaction proceeded for
the predetermined time, the reaction was switched to ethylene
homopolymerization phase. The circulating gas introduced into the
bottom inlet of the reactor contained hydrogen, nitrogen, methane,
ethane, ethylene, 1-hexene, and a small amount of isopentane, and
had a pressure of 3.6 MPa and a temperature of 96.degree. C. After
the circulating gas was circulated for multiple times, the
circulating gas discharged from a heat exchange did not contain the
condensate, and had a gas density of 27.2 kg/m.sup.3. After
gas-liquid separation, .alpha.-olefin and isopentane (accounting
for 80% of the circulating gas flow) were introduced into a
material storage tank, and a small amount of the condensate and
.alpha.-olefin that did not go through gas-liquid separation was
introduced, together with the circulating gas, into the fluidized
bed reactor. The gaseous polymerization ran for 12 min (including
the operation time for process switching).
Then, the reaction was switched from ethylene homopolymerization to
ethylene/1-hexene copolymerization. A condensate comprising
1-hexene and isopentane was introduced through a feed pump into the
reactor from the upper portion of the distribution plate of the
reactor bed. The polymerization temperature at the lower portion
gradually decreased to 75.degree. C. The copolymerization reaction
at this stage proceeded for 8 min.
The above operations were carried out sequentially and alternately
and the polymerization was carried out for 3 hours in total.
Polyethylene (b) was thus obtained.
Polyethylene (b) was subjected to temperature rising elution
fractionation testing, thermal fractionation by successive
self-nucleation/annealing (SSA) testing, and other property
testing, respectively. The amounts of fractions at different
temperatures were shown in Table 1. Results of thermal
fractionation by successive self-nucleation/annealing (SSA) testing
were shown in Table 2, and results of other property testing were
shown in Table 3.
EXAMPLE 3
Ethylene homopolymerization and ethylene/1-hexene copolymerization
were carried out in a fluidized bed reactor to prepare the
polyethylene material of the present application. The fluidized bed
reactor was filled with a catalyst system of Ziegler-Natta catalyst
and triethylaluminum. A reaction material gas (containing hydrogen,
nitrogen, methane, ethane, ethylene, 1-hexene, and a small amount
of isopentane) and a condensate isopentane (containing 1-hexene)
were introduced into the reactor through its bottom inlet where the
temperature was 56.degree. C., and ethylene/1-hexene
copolymerization reaction was first carried out. The rest gas after
the reaction was used as a circulating gas and was discharged out
of the reactor through its top outlet. The circulating gas was then
compressed, condensed, and subjected to gas-liquid separation. The
liquid material flow resulted from gas-liquid separation was stored
in a 1-hexene storage tank, and meanwhile the gas resulted from
gas-liquid separation was used as circulating gas and was
circulated into the reactor through a reactor feed inlet for
continued reaction. When the circulating gas was introduced into
the bottom portion of the reactor bed, it was a mixture of gas and
liquid. The liquid in the fluidized bed had a mass fraction of 30
wt %, and a superficial fluidizing gas velocity was 0.62 m/s. A
polymerization temperature at the bottom portion of the bed
(gas-liquid-solid reaction zone) was 70.degree. C., while a
polymerization temperature at the top portion of the bed (gas-solid
reaction zone) was 84.degree. C. In the circulating gas, the dew
point temperature of liquid isopentane was between the temperature
of the bottom portion and the temperature of the top portion of the
bed. The copolymerization proceeded for 8 min.
After the copolymerization polymerization reaction proceeded for
the predetermined time, the reaction was switched to ethylene
homopolymerization phase. The circulating gas introduced into the
bottom inlet of the reactor contained hydrogen, nitrogen, methane,
ethane, ethylene, 1-hexene, and a small amount of isopentane, and
had a pressure of 2.6 MPa and a temperature of 88.degree. C. After
the circulating gas was circulated for multiple times, the
circulating gas discharged from a heat exchange did not contain the
condensate, and had a gas density of 28.2 kg/m.sup.3. After
gas-liquid separation, 1-hexene and isopentane (accounting for 80%
of the circulating gas flow) were introduced into a material
storage tank, and a small amount of the condensate and 1-hexene
that did not go through gas-liquid separation was introduced,
together with the circulating gas, into the fluidized bed reactor.
The gaseous polymerization ran for 8 min (including the operation
time for process switching).
Then, the reaction was switched from ethylene homopolymerization to
ethylene/1-hexene copolymerization. A condensate comprising
1-hexene and isopentane was introduced through a feed pump into the
reactor from the upper portion of the distribution plate of the
reactor bed. The polymerization temperature at the lower portion
gradually decreased to 70.degree. C. The copolymerization reaction
at this stage proceeded for 12 min.
The above operations were carried out sequentially and alternately
and the polymerization was carried out for 2.5 hours in total.
Polyethylene (c) was thus obtained.
Polyethylene (c) was subjected to temperature rising elution
fractionation testing, thermal fractionation by successive
self-nucleation/annealing (SSA) testing, and other property
testing, respectively. The amounts of fractions at different
temperatures were shown in Table 1. Results of successive
self-nucleation/annealing (SSA) thermal fractionation testing were
shown in Table 2, and results of other property testing were shown
in Table 3.
EXAMPLE 4
Ethylene homopolymerization and ethylene/1-butene/1-hexene
copolymerization were carried out in a fluidized bed reactor to
prepare the polyethylene material of the present application. The
fluidized bed reactor was filled with a catalyst system of
Ziegler-Natta catalyst and triethylaluminum. A reaction material
gas (containing hydrogen, nitrogen, methane, ethane, ethylene,
1-butene, 1-hexene, and a small amount of isopentane) and a
condensate isopentane (containing 1-hexene) were introduced into
the reactor through its bottom inlet where the temperature was
56.degree. C., and ethylene/1-butene/1-hexene copolymerization
reaction was first carried out. The rest gas after the reaction was
used as a circulating gas and was discharged out of the reactor
through its top outlet. The circulating gas was then compressed,
condensed, and subjected to gas-liquid separation. The liquid
material flow resulted from the gas-liquid separation was stored in
a 1-hexene storage tank, and meanwhile the gas resulted from the
gas-liquid separation was used as circulating gas and was
circulated into the reactor through a reactor feed inlet for
continued reaction. When the circulating gas was introduced into
the bottom portion of the reactor bed, it was a mixture of gas and
liquid. The liquid in the fluidized bed had a mass fraction of 26
wt %, and a superficial fluidizing gas velocity was 0.58 m/s. A
polymerization temperature at the bottom portion of the bed
(gas-liquid-solid reaction zone) was 70.degree. C., while a
polymerization temperature at the top portion of the bed (gas-solid
reaction zone) was 86.degree. C. In the circulating gas, the dew
point temperature of liquid isopentane was between the temperature
of the bottom portion and the temperature of the top portion of the
bed. The copolymerization proceeded for 8 min.
After the copolymerization polymerization reaction proceeded for
the predetermined time, the reaction was switched to ethylene
homopolymerization phase. The circulating gas introduced into the
bottom inlet of the reactor contained hydrogen, nitrogen, methane,
ethane, ethylene, 1-butene, and a small amount of isopentane, and
had a pressure of 2.6 MPa and a temperature of 78.degree. C. After
the circulating gas was circulated for multiple times, the
circulating gas discharged from a heat exchange did not contain the
condensate, and had a gas density of 26.2 kg/m.sup.3. After
gas-liquid separation, .alpha.-olefin and isopentane (accounting
for 80% of the circulating gas flow) were introduced into a
material storage tank, and a small amount of the condensate and
1-butene that did not go through gas-liquid separation was
introduced, together with the circulating gas, into the fluidized
bed reactor. The gaseous polymerization ran for 16 min (including
the operation time for process switching).
Then, the reaction was switched from ethylene homopolymerization to
ethylene/1-butene/1-hexene copolymerization. A condensate
comprising 1-hexene and isopentane was introduced through a feed
pump into the reactor from the upper portion of the distribution
plate of the reactor bed. The polymerization temperature at the
lower portion gradually decreased to 70.degree. C. The
copolymerization reaction at this stage proceeded for 12 min.
The above operations were carried out sequentially and alternately
and the polymerization was carried out for 3.5 hours in total.
Polyethylene (d) was thus obtained.
Polyethylene (d) was subjected to temperature rising elution
fractionation testing, thermal fractionation by successive
self-nucleation/annealing (SSA) testing, and other property
testing, respectively. The amounts of fractions at different
temperatures were shown in Table 1. Results of thermal
fractionation by successive self-nucleation/annealing (SSA) testing
were shown in Table 2, and results of other property testing were
shown in Table 3.
EXAMPLE 5
Ethylene homopolymerization and ethylene/1-hexene/1-octene
copolymerization were carried out in a fluidized bed reactor to
prepare the polyethylene material of the present application. The
fluidized bed reactor was filled with a catalyst system of
Ziegler-Natta catalyst and triethylaluminum.
A reaction material gas (containing hydrogen, nitrogen, methane,
ethane, ethylene, 1-octene, and a small amount of isopentane) and a
condensate isopentane (containing 1-octene) were introduced into
the reactor through its bottom inlet where the temperature was
62.degree. C., and ethylene/l-octene copolymerization reaction was
first carried out. The rest gas after the reaction was used as a
circulating gas and was guided out of the reactor through its top
outlet. The circulating gas was then compressed, condensed, and
subjected to gas-liquid separation. The liquid material flow
resulted from gas-liquid separation was stored in a 1-octene
storage tank, and meanwhile the gas resulted from gas-liquid
separation was used as circulating gas and was circulated into the
reactor through a reactor feed inlet for continued reaction. When
the circulating gas was introduced into the bottom portion of the
reactor bed, it was a mixture of gas and liquid. The liquid in the
fluidized bed had a mass fraction of 26 wt %, and a superficial
fluidizing gas velocity was 0.66 m/s. A polymerization temperature
at the bottom portion of the bed (gas-liquid-solid reaction zone)
was 66.degree. C., while a polymerization temperature at the top
portion of the bed (gas-solid reaction zone) was 90.degree. C. In
the circulating gas, the dew point temperature of liquid isopentane
was between the temperature of the bottom portion and the
temperature of the top portion of the bed. The copolymerization
proceeded for 10 min.
After the ethylene/1-octene copolymerization polymerization
reaction proceeded for the predetermined time, the reaction was
switched to ethylene homopolymerization phase. The circulating gas
introduced into the bottom inlet of the reactor contained hydrogen,
nitrogen, methane, ethane, ethylene, 1-octene, and a small amount
of isopentane, and had a pressure of 2.6 MPa and a temperature of
96.degree. C. After the circulating gas was circulated for multiple
times, the circulating gas discharged from a heat exchange did not
contain the condensate, and had a gas density of 26.2 kg/m.sup.3.
After gas-liquid separation, .alpha.-olefin and isopentane
(accounting for 80% of the circulating gas flow) were introduced
into a material storage tank, and a small amount of the condensate
and 1-octene that did not go through gas-liquid separation was
introduced, together with the circulating gas, into the fluidized
bed reactor. The gaseous polymerization ran for 10 min (including
the operation time for process switching).
Then, the reaction was switched to ethylene/1-hexene
copolymerization. The above circulating gas was circulated into the
reactor through a bottom feed inlet for continued reaction, and
meanwhile 1-hexene and a condensate were also introduced. The rest
gas after the reaction was used as a circulating gas and was
discharged out of the reactor through its top outlet. The
circulating gas was then compressed, condensed, and subjected to
gas-liquid separation. The liquid material flow resulted from
gas-liquid separation was stored in a 1-hexene storage tank, and
meanwhile the gas resulted from gas-liquid separation was used as
circulating gas and was circulated into the reactor through a
reactor feed inlet for continued reaction. When the circulating gas
was introduced into the bottom portion of the reactor bed, it was a
mixture of gas and liquid. The liquid in the fluidized bed had a
mass fraction of 29 wt %, and a superficial fluidizing gas velocity
was 0.72 m/s. A polymerization temperature at the bottom portion of
the bed (gas-liquid-solid reaction zone) was 70.degree. C., while a
polymerization temperature at the top portion of the bed (gas-solid
reaction zone) was 88.degree. C. In the circulating gas, the dew
point temperature of liquid isopentane was between the temperature
of the bottom portion and the temperature of the top portion of the
bed. The copolymerization proceeded for 8 min.
After the ethylene/1-hexene copolymerization polymerization
reaction proceeded for the predetermined time, the reaction was
switched to ethylene homopolymerization phase. The circulating gas
introduced into the bottom inlet of the reactor contained hydrogen,
nitrogen, methane, ethane, ethylene, 1-hexene, and a small amount
of isopentane, and had a pressure of 2.8 MPa and a temperature of
96.degree. C. After the circulating gas was circulated for multiple
times, the circulating gas discharged from a heat exchange did not
contain the condensate, and had a gas density of 26.8 kg/m.sup.3.
After gas-liquid separation, .alpha.-olefin and isopentane
(accounting for 80% of the circulating gas flow) were introduced
into a material storage tank, and a small amount of the condensate
and 1-hexene that did not go through gas-liquid separation was
introduced, together with the circulating gas, into the fluidized
bed reactor. The gaseous polymerization ran for 8 min (including
the operation time for process switching).
Then, the reaction was switched from ethylene homopolymerization to
ethylene/1-octene copolymerization. A condensate comprising
1-octene and isopentane was introduced through a feed pump into the
reactor from the upper portion of the distribution plate of the
reactor bed. The polymerization temperature at the lower portion
gradually decreased to 66.degree. C. The copolymerization reaction
at this stage proceeded for 10 min.
The above operations were carried out sequentially and alternately
and the polymerization was carried out for 4.5 hours. Polyethylene
(e) was thus obtained.
Polyethylene (e) was subjected to temperature rising elution
fractionation testing, thermal fractionation by successive
self-nucleation/annealing (SSA) testing, and other property
testing, respectively. The amounts of fractions at different
temperatures were shown in Table 1. Results of thermal
fractionation by successive self-nucleation/annealing (SSA) testing
were shown in Table 2, and results of other property testing were
shown in Table 3.
COMPARATIVE EXAMPLE 1
In accordance with the method described in the examples of patent
application CN200580027288, in a single reactor system, a double
peak polyethylene resin product was prepared by gaseous
polymerization and by using a spray-dried catalyst system. In this
comparative example, a spray-dried catalyst composition was
suspended in a mixture of mineral oil and hexane to obtain a
catalyst slurry for injection into a fluidized bed reactor. Typical
reaction conditions were: a polymerization temperature being
85.degree. C.-100.degree. C., a content of hexene comonomer being
about 0.007 (C6:C2 molar ratio), and H2:C2 molar ratio being
0.0035. Double peak polyethylene (f) prepared by this method had a
density of about 0.946, and a spread of up to 95.
Polyethylene (f) was subjected to temperature rising elution
fractionation testing, thermal fractionation by successive
self-nucleation/annealing (SSA) testing, and other property
testing, respectively. The amounts of fractions at different
temperatures were shown in Table 1. Results of thermal
fractionation by successive self-nucleation/annealing (SSA) testing
were shown in Table 2, and results of other property testing were
shown in Table 3.
COMPARATIVE EXAMPLE 2
An industrial fluidized bed olefin polymerization reactor having a
diameter of 3 m and a cylinder height of 12 m was used. 1-butene
was used as a comonomer. Reactants comprised: 30.12 vol % ethylene,
6.98 vol % 1-butane, 6.30 vol % hydrogen. A promoter
methylaluminoxane having a concentration of 300 ppm was added into
the reactor, followed by starting a catalyst feed unit which then
fed a metallocene catalyst into the fluidized bed reactor at a flow
rate of 1.0 kg/hr. By using this gaseous polymerization method,
metallocene polyethylene (g) was prepared.
Polyethylene (g) was subjected to temperature rising elution
fractionation testing, thermal fractionation by successive
self-nucleation/annealing (SSA) testing, and other property
testing, respectively. The amounts of fractions at different
temperatures were shown in Table 1. Results of thermal
fractionation by successive self-nucleation/annealing (SSA testing
were shown in Table 2, and results of other property testing were
shown in Table 3.
COMPARATIVE EXAMPLE 3
Degree of branching of polyethylene Brand 1820 prepared by Shandong
Qilu Petrochemical Engineering Co. Ltd was analyzed by using the
same method as used in Example 1 for analyzing degree of branching.
The polyethylene in this example was prepared by gaseous
polymerization in a fluidized bed reactor using ethylene as a
material, 1-butene as a comonomer, and hydrogen as a chain transfer
agent.
TABLE-US-00001 TABLE 1 Results of fractionation of polyethylene by
temperature rising elution Amount of Fraction (wt %) Grade of
Comparative Comparative Fraction Example 1 Example 2 Example 3
Example 4 Example 5 Example 1 Example 2 (Fractionated by
Polyethylene Polyethylene Polyethylene Polyethylene Polyethylene
Polye- thylene Polyethylene Temperature) (a) (b) (c) (d) (e) (f)
(g) 40.degree. C. 16.3 15.4 13.1 11.9 10.6 4.5 0.0 50.degree. C.
13.6 12.5 11.5 10.4 11.3 6.6 0.0 60.degree. C. 11.6 10.9 9.9 10.8
12.4 9.7 0.0 70.degree. C. 12.3 11.5 11.9 12.1 13.4 11.5 0.2
80.degree. C. 13.3 12.9 14.2 15.7 14.7 13.9 0.2 90.degree. C. 12.5
13.7 16.3 14.8 12.9 16.0 0.3 100.degree. C. 11.5 12.2 12.4 13.5
12.9 18.0 0.3 110.degree. C. 9.9 10.9 10.7 10.8 11.8 19.8 99.0
Standard 1.94% 1.61% 2.33% 2.07% 2.18% 5.76% 35.2% Deviation S
TABLE-US-00002 TABLE 2 Results of thermal fractionation of
polyethylene by successive self-nucleation/annealing a b Fractions
T.sub.m/.degree. C. f.sub.i/% l/nm MSL T.sub.m/.degree. C.
f.sub.i/% l/nm MSL P1 89.41 13.47 4.55 41.46 89.1 15.73 4.52 41.16
P2 100.15 6.42 5.62 54.83 100.47 6.99 5.66 55.34 P3 105.33 8.11
6.34 64.34 105.58 8.73 6.38 64.87 P4 110.53 10.69 7.29 77.37 110.77
11.09 7.34 78.09 P5 116.02 13.62 8.64 97.56 116.18 13.94 8.69 98.29
P6 121.35 15.50 10.54 129.24 121.6 17.21 10.65 131.21 P7 127.45
32.19 14.10 201.69 127.86 26.30 14.43 209.43 c d Fractions
Tm/.degree. C. f.sub.i/% l/nm MSL Tm/.degree. C. f.sub.i/% l/nm MSL
P1 89.21 16.76 4.59 41.45 89.34 16.71 4.43 41.34 P2 100.45 6.34
5.65 54.89 100.54 6.33 5.45 54.23 P3 105.54 8.34 6.32 65.43 105.94
8.54 6.76 66.54 P4 110.67 10.77 7.54 78.45 110.45 10.45 7.45 78.76
P5 116.97 13.08 8.67 99.65 116.76 13.06 8.87 99.34 P6 121.34 15.21
11.73 134.65 121.46 1512 11.31 132.32 P7 127.55 32.45 14.99 211.76
127.23 32.34 15.12 212.54 e f Fractions Tm/.degree. C. f.sub.i/%
l/nm MSL Tm/.degree. C. f.sub.i/% l/nm MSL P1 88.66 9.45 4.23 40.11
90.07 9.26 4.60 42.11 P2 98.67 7.89 5.23 52.90 100.91 5.01 5.72
56.06 P3 105.34 8.87 6.21 63.68 106 6.32 6.45 65.78 P4 108.79 8.98
7.13 75.08 111.18 8.43 7.42 79.34 P5 113.60 12.65 8.56 99.09 116.76
12.10 8.86 101.05 P6 118.79 14.87 10.57 132.78 122.35 15.05 11.00
137.46 P7 125.09 37.29 14.07 231.05 129.08 43.83 15.49 236.28 g
Fractions Tm/.degree. C. f.sub.i/% l/nm MSL P1 -- -- -- -- P2 -- --
-- -- P3 -- -- -- -- P4 -- -- -- -- P5 -- -- -- -- P6 -- -- -- --
P7 118.69 99.56 8.87 103.54 Notes: Tm represents melting
temperature; fi represents the relative amount of each fraction; l
represents number-average lamella thickness; and MSL represents
methylene sequence length.
TABLE-US-00003 TABLE 3 Index of physical properties of polyethylene
Comparative Comparative Example 1 Example 2 Example 3 Example 4
Example 5 Example 1 Example 2 Polyethylene Polyethylene
Polyethylene Polyethylene Polyethylene Polyethy- lene Polyethylene
Determination (a) (b) (c) (d) (e) (f) (g) Methods Density
(g/cm.sup.3) 0.902 0.921 0.929 0.942 0.894 0.944 0.917 GB/T1033- 70
Melt Flow Rate 0.81 0.98 0.91 0.84 0.99 1.51 1.82 GB/T3682- (g/10
min) 83 Tensile Yield 19 21 22 24 23 18 17 GB/T1040- Strength (MPa)
79 Elongation at 700 710 650 650 720 520 350 GB/T1040- Break (%) 79
Melting 123 128 130 135 121 128 118 GB/T4608- Temperature 84
(.degree. C.) Haze (%) 11.6 10.5 12.4 11.9 10.9 12.5 11.0 GB/T2410-
80 Falling Dart 206 214.6 209.5 218 223.6 234.5 215.0 GB/T9639-
Impact Strength 88 (g) Weight-average 126821 134698 137925 146658
129836 174255 123506 -- Molecular Weight Molecular 3.62 3.42 3.64
3.57 3.73 7.19 1.21 -- Weight Distribution Coefficient (PDI)
TABLE-US-00004 TABLE 4 Number-average Weight-average Distribution
Lamella Lamella Coefficient Samples Thickness l.sub.n/nm Thickness
l.sub.w/nm I Example 1 9.32 10.71 1.149 (Polymer a)
It can be seen from Table 1 that each of the polyethylene (a)-(e)
prepared by the method of the present application has a fraction
amount (of temperature rising elution fractionation) at 40.degree.
C. in a range of 9.0%-40.0%, and a standard deviation of two
fractions at temperatures at an interval of 10.degree. C. from
40.degree. C. to 110.degree. C. in a range of 0%-6.0%. The
polyethylene (f) prepared in comparative example 1 has a fraction
amount at 40.degree. C. that is not in the range of 9.0%-40.0%. The
polyethylene (g) prepared by the method of the comparative example
2 was prepared by using a metallocene catalyst; its molecular
weight distribution coefficient is very small (PDI=1.1); its
fraction amount at 40.degree. C. is 0%, and a standard deviation of
its fractions at temperatures from 40.degree. C. to 110.degree. C.
is 35.1%, not in the range reasonably sought to be protected by the
present application.
As can be found from the data of Table 2, lamella thickness
distributions of polyethylene (a)-(e) prepared by the method of the
present application are similar, and the lamella thickness of the
fraction (high-molecular-weight fraction) of P7 is in a range of 14
nm-15 nm, which is smaller than the lamella thickness of
polyethylene (f) and the lamella thickness of polyethylene (g).
This indicates that the polyethylene prepared by the method of the
present application has a wider branching distribution, and that
the high-molecular-weight fraction has a dramatically improved
branching amount. The mechanical property of the product is thus
greatly improved.
As can be found further from Table 2, the amounts of the fraction
P1 (low-molecular-weight fraction) of the polyethylene (a)-(e)
prepared by the method of the present application are higher than
those of polyethylene (f), and polyethylene (g), which is
consistent with the data of temperature rising elution
fractionation shown in Table 1. The increase of the amount of the
low-molecular-weight fraction increases the machinability of
products and enables the polyethylene product prepared by the
present application to be better used in forming and machining.
When the data of Table 1 and the data of Table 3 are compared, it
is found that the polyethylenes (a), (b), (c), (d), and (e)
prepared by the method of the present application have obvious
property advantage over the polyethylene (f) prepared by the method
of comparative example 1 and the metallocene polyethylene g
prepared in comparative example 2 in melt flow index, tensile yield
strength, elongation at break, and falling dart impact
strength.
When analyzed from the perspective of chain structure, the
polyethylene prepared by the method of the present application is
primarily characterized by the distinct improvement of amount of
the low-molecular-weight fraction and the dramatic increase of the
branching amount of the high-molecular-weight fraction. The
mechanical strength of polyethylene depends mainly on the
high-molecular-weight fraction. Branches in the
high-molecular-weight fraction enhance the entwining among tie
molecules, thereby improving the tensile strength of products.
It can be seen from FIG. 1 that branches of the polyethylene
prepared by the traditional gaseous polymerization are distributed
on molecular chains with a molecular weight of less than 110000,
while the distribution of branches of the polyethylene prepared by
the present application reaches molecular chains with a molecular
weight of 150000, as a result of which, the branches are
distributed widely between molecular chains, and the amount of
branches in the high-molecular-weight fraction is greatly
increased.
Analyzed from the perspective of crystalline structure, the
low-molecular-weight fraction and the high-degree branching
fraction of the polyethylene prepared by the method of the present
application play an important role in the nucleation; crystal
grains of sphere crystals of the entire polymer are therefore more
in number and smaller in sizes. For polyethylene, properties
thereof are significantly influenced by the size of the sphere
crystals. In general, the smaller the size of the sphere crystal
is, the lower the haze of the polyethylene is, i.e., the higher the
transparency thereof is; the smaller the size of the sphere crystal
is, the higher the impact strength of the polyethylene is.
Although the present application has been explained in detail as
above, for one skilled in the art, it would be obvious to make any
variations within the spirit and protection scope of the present
application. It shall also be appreciated that those various
aspects, different parts of different examples, and those features
recited in the present application are all combinable with one
another or wholly or entirely exchangeable between each other. In
the specific examples described above, those examples referring to
another specific example may be combined with another example in a
suitable manner, which would be apprehensible by one skilled in the
art. In addition, one skilled in the art shall further be
appreciated that the foregoing descriptions are merely exemplary
examples of the present application, and are not intended for
limiting the present application.
* * * * *